Knowing the location of a mobile device, such as a mobile phone, personal data assistant (PDA), cellular phone, and the like, may be useful because the location of the mobile device typically is the same as the location of the user of the device. With knowledge of the location of a user, for example, emergency personnel may be dispatched to the user in an emergency, or the user can get directions if lost, or advertisements related to the location of the user can be sent to the user's mobile device. For example, if the user is near a coffee shop, an advertisement or message can be sent to the user's device to entice the user into the coffee shop. If the user is having dinner in a restaurant, an advertisement or message for an ice cream stand next door can be sent to the user's device.
There are many methods in the prior art that can be used to locate a mobile device, including the Global Positioning System (GPS), time difference of arrival (TDOA), cell identification (cell ID), enhanced cell ID (E-CID), and angle of arrival (AOA), to name a few. Some location techniques like GPS, however, require hardware and software to be added to the mobile device. Thus, a device that does not include the GPS hardware and software cannot be located using GPS. Other techniques, such as TDOA or AOA, for example, require hardware and software to be added to the cell network at, for example, the cellular antenna, base transceiver stations, base station controllers, etc. But such installations may be expensive. Further, all of these location techniques may lack the accuracy necessary to, for example, send targeted advertisements or messages. For example, if the user is in a shopping mall, the user's mobile device may not be able to receive GPS signals, making it impossible to determine the device's location within the mall. And while TDOA may be used to estimate a device's location within the shopping mall, the accuracy requirements for TDOA may not enable determining whether the phone is closer to a clothing store versus a coffee shop versus a music store. Thus, sending targeted advertisements or messages may be fruitless.
While the foregoing techniques discussed so far estimate locations based on signals that the mobile device sends (e.g., TDOA) or on signals that the mobile device receives (e.g., GPS), another location technique takes advantage of the mobile device's environment to estimate its location. Thus, instead of processing signals sent by the mobile device or sent to the mobile device for the specific purpose of determining its location, these techniques process other information. For example, a mobile device may capture environmental light or movement information through an accelerometer and use that information to determine that the phone is in a disco or a movie theater.
However, the use of environmental information may require surveying potential mobile device locations in advance and storing the environmental information associated with those locations. Further, estimating a mobile device's location based on the vast amount of this environment information data may involve comparing the environmental information perceived by the mobile device with the stored information in an attempt to find similarities or a “match.” Such comparison can absorb vast amounts of computer resources and may not be capable of completing a location estimation in a reasonable amount of time.